This invention relates to colloidal size particulates containing particles of an inorganic material and to polymerization processes used to prepare such particulates.
Pigments, fillers, metal oxides and other inorganic particulates that tend to agglomerate are often coated with or encapsulated in hydrophobic polymers. These coated or encapsulated particles are often used in a wide variety of applications such as electroconductive additives to plastics, toners in electrophotographic applications, pigmented paints as well as many other applications.
Conventionally, such particulates are prepared by (1) treating the inorganic solid with acid, a combination of acid and base, alcohol or a polymer solution; (2) dispersing an addition polymerizable monomer in an aqueous dispersion of a treated inorganic solid and (3) subjecting the resulting dispersion to emulsion polymerization conditions. Examples of such methods are described in U.S. Pat. Nos. 4,048,136; 3,383,346; 3,935,340; 3,544,500 and 3,884,871. Unfortunately, these methods are deficient in that they often require expensive multi-step procedures, anchoring agents, functional additives, stabilizing agents and the like. Also, the polymeric particulates often must be employed as viscous pastes or dry powders. Furthermore, such aforementioned processes do not involve the preparation of metal particles which are encapsulated with hydrophobic polymers. In addition, such aforementioned processes introduce problems such as agglomeration of metal particles and oxidation of metal particles in numerous circumstances.
The in situ encapsulation of various magnetic metals through the decomposition of the respective metal carbonyls in a toluene solution of rubbery polymers is disclosed in U.S. Pat. No. 3,228,881. Such a type of process is described by Hess et al., Applied Polymer Science, Vol. 10, page 1915 (1966). Unfortunately, the use of such a type of process includes limitations which include, for example, the fact that highly diluted solvent base systems are employed; the processes related to magnetic metals only; and the dimensions and shapes of the formed metal particles are difficult to predict and control.
The preparation of a catalyst composition comprising colloidal rhodium encapsulated in polyvinylalcohol is disclosed in J. Macromol. Sci.--Chem., Vol. A (12) page 1117 (1978). Unfortunately, the disclosed compositions are useful in a limited number of applications.
In view of the deficiencies of the prior art, it would be highly desirable to provide a process for providing preformed, powdered, submicron size metal (both magnetic and nonmagnetic) particles dispersed in a substantially non-agglomerated manner in hydrophobic polymers.